Blasting techniques are frequently used to remove or strip coatings from an underlying surface of a workpiece or other substrate. A variety of blasting techniques are known that involve both abrasive and non-abrasive media, where the media is blasted onto a coated substrate at high velocity to remove or alter the coating. High pressure air is typically used as the carrier fluid to provide the driving force to propel the media at the velocities needed to remove a coating. Some blasting systems use a pressurized mix of the media and air while other systems use the venturi effect where high pressure air is passed over a container of the media to create a suction that feeds the media into the flowing air stream. Blasting media varies with the particular coating that is to be removed or treated, however, known media include sand, plastic, glass, water, steel shot, and vegetable based specialty media, such as, cornstarch or soybean blasting media.
Although blasting using robotics is known, many blasting applications necessarily require manual manipulation of a blast nozzle by a human operator. In these applications, the user holds the nozzle by hand and directs the blast media exiting the nozzle at the work surface. The distance as measured from the nozzle outlet to the surface of the workpiece is commonly referred to as the “stand-off” distance. The stand-off distance is directly proportional to the energy of the blasting media as it impacts the workpiece surface. The closer the nozzle is to the surface the greater the velocity of the media at impact. Stand-off distances can be visually estimated by the operator or visually determined using a targeting system that employs one or more lasers. These prior targeting systems typically rely on a combination of a gauge beam and a reference beam in order to set a desired stand-off distance, where only the single reference beam is adjustable. The correct or appropriate stand-off distance is usually a function of several factors, such as, the type of coating to be removed or treated, the type of blast media, the composition of the underlying substrate, the gas pressure of the carrier fluid, and/or the chemical composition of the coating. In many cases the correct stand-off distance is determined by a trial and error approach.
Once the appropriate stand-off distance is determined, the user will work the nozzle around the workpiece to blast the coating. If the nozzle is held too close, the blasting media may damage the underlying workpiece and, if held too far away, there will not be sufficient velocity of the blast media to accomplish the desired amount of treatment or sufficient removal of the coating. Likewise, repeated failure to maintain the stand-off distance, usually caused by improper operator technique during the blasting operation, can yield inconsistent results. Curved and/or contoured surfaces of the workpiece can also contribute to the failure to consistently maintain the proper effective stand-off distance. In sum, operator attentiveness to this parameter can be highly subjective and unreliable.
In general, abrasive blasting presents technical challenges with regard to the most effective and efficient use of the chosen blast media. The quality of the finished part or workpiece depends on the operator's ability to apply the abrasive evenly, but even with a skilled operator there are visibility challenges created by the blast media delivered via pressurized air since dust and debris will rapidly fill the cabinet or blasting area, making it difficult to ensure that the part is being uniformly covered. Stationary incandescent lights mounted in the cabinet and nozzle-mounted lights have been attempted to address some of the visibility problems encountered during blasting procedures. However, in a number of applications such lighting can actually add to the overall visibility problem by illuminating the dust cloud, which then reflects light back to the operator's eyes further reducing visibility of the blasting surface. Although automated/robotic systems have addressed the problem of achieving repeatable uniform coverage to a degree, such systems are large, cumbersome, and expensive, and not readily applicable to hand-held blasting systems.
Accordingly, a need exists to provide a reliable, low cost targeting apparatus to ensure that the appropriate stand-off distance is maintained by an operator using a hand-held blasting apparatus. Preferably such an apparatus would also incorporate an optional task lighting feature that would provide a light source in close proximity to the blast media impact area to avoid or greatly reduce light scatter caused by suspended dust and debris. Such a targeting apparatus would allow the operator to readily maintain the appropriate stand-off distance during the blasting procedure regardless of the shape of the workpiece and would significantly increase the efficiency of the blasting procedure, thus reducing operating costs, while greatly reducing the risk of causing damage to the underlying surface of the workpiece.